Being green comes at a cost - Porirua City Council spent $46,713 on pot plants in the year to March 2012.

That compares to $30,000 spent by Wellington City Council on indoor plants the same year.

Porirua's costs relate to indoor plants in the council's office blocks and at public spaces such as Pataka, Te Rauparaha Arena, the central library, the i-Site, Gear Homestead and Whenua Tapu crematorium, for a total of 322 plants.

The figure does not include outdoor plants or the flower towers under the Canopies.

The amount is a shock and will be investigated, says the council's acting chief executive, David Rolfe.

"When we saw those figures we were surprised it cost so much and we'll look at seeing if we can reduce our costs. We're always looking at our expenditure, we have budgets, but I think this one wasn't actually identified as a cost to look at. These things can creep away on you."

Wellington City Council's spend only related to its council offices, not public spaces, Mr Rolfe says.

"It's not a fair comparison between the two, in that we provide probably nine different sites, not just the council building, and I'm sure they all add to the experience."

All Porirua City Council's plants are from its own nursery, which saves money, Mr Rolfe says. Each plant is watered once a week.

The council will try to reduce costs but won't get rid of its indoor foliage, he says.

"It provides a pleasant environment for staff, and they actually improve air quality."